1988 Volvo 740 non-turbo with 223,000 miles on it
Car just started to idle rough when stopped at light or stop sign and the transmission is engaged in Drive or Reverse. Idle smooths out when put in Neutral or Park. Just replaced the spark plugs, wires and O2 sensor. Disconnected and re-connected the battery trying to re-set the computer. It improved a little but stills idle rough. Before I did the work I did notice the rough idle went away after I filled the gas tank but returned when it got to about 3/4 of a tank. I have a locking gas cap with a feature that releases pressure from the gas tank when the key is inserted. I know that a faulty gas cap on a Fuel Injected engine can cause problems.
Also how do you reset the " Service" idiot light?